57Fe NMR characterisation of pyrrhotite

Abstract The detection of pyrrhotite (Fe 7 S 8 ) by 57 Fe NMR spectroscopy in zero applied field is reported. The 57 Fe signal of pyrrhotite is detected in zero field using two different methods, with both yielding peak signal at 42.03 MHz. The technique and theory of 57 Fe NMR spectroscopy of ferromagnetic iron compounds in zero applied field has recently been reviewed, and a zero field NMR ore detection and separation method has been recently described. The method presented here can be suitably adapted for detection and selection of pyrrhotite-containing ore fragments enriched in Fe 7 S 8 in mining applications. The association of pyrrhotite with the Ni-rich mineral pentlandite (Fe,Ni) 9 S 8 enables peak signal detection at 42.03 MHz as a proxy for nickel-rich material in ultramafic nickel sulphide deposits.